Chip scale packages and methods for manufacturing the chip scale packages at wafer level

ABSTRACT

In accordance with the present invention, a chip scale package (CSP) is manufactured at wafer-level. The CSP includes a chip, a conductor layer for redistribution of the chip pads of the chip, one or two insulation layers and multiple bumps, which are interconnected to respective chip pads by the conductor layer and are the terminals of the CSP. In addition, in order to improve the reliability of the CSP, a reinforcing layer, an edge protection layer and a chip protection layer is provided. The reinforcing layer absorbs stress applied to the bumps when the CSP are mounted on a circuit board and used for an extended period, and extends the life of the bumps, and thus, the life of the CSP. The edge protection layer and the chip protection layer prevent external force from damaging the CSP. After forming all elements constituting the CSP on the semiconductor wafer, the semiconductor wafer is sawed to produce individual CSPs.

BACKGROUND

1. Field of the Invention

This invention relates to chip scale packages and methods formanufacturing the packages at wafer level.

2. Description of Related Art

Miniaturization of electronic devices, which is one of major trends inthe electronics industry, has led to the development of manytechnologies for manufacturing small packages, especially packages thathave almost the same size as semiconductor integrated circuit chips. TheJoint Electronic Device Engineering Council (JEDEC) has proposed thename ‘Chip Scale Package (CSP)’ for a type of small packages. JEDEC'sdefinition of the CSP is a package having an outline that is 1.2 timesor less than the outline of the semiconductor chip included in thepackage.

Many companies and institutes have developed their own CSP manufacturingtechnologies, and some have commercialized their own technologies orproducts. However, most of the newly developed CSPs have severaldrawbacks in the areas of product reliability, process reliability andmanufacturing cost, when compared to plastic packages which are wellestablished in the semiconductor industry. Therefore, forcommercializing CSPs widely and successfully, new CSPs that have betterprocess and product reliability and lower manufacturing costs aresought.

SUMMARY

In accordance with the present invention, a chip scale package (CSP) ismanufactured at wafer-level. The CSP includes a conductor layer forredistribution of the chip pads on a semiconductor chip, one or twoinsulation layers and solder bumps which function as the terminals ofthe CSP and are interconnected to respective chip pads by the conductorlayer. In one embodiment, the conductor layer is formed directly on thesurface or passivation layer of the semiconductor wafer, and in anotherembodiment, after an insulation layer is formed on the surface of thesemiconductor wafer, the conductor layer is formed on the insulationlayer. In both embodiments, another insulation layer is formed on theconductor layer, and additional metal layers can be formed between thechip pads and the conductor layer, and between the solder bumps and theconductor layer for improving the interface integrity.

In addition, in order to improve the reliability of the CSP, areinforcing layer, an edge protection layer and a chip protection layerare provided. The reinforcing layer, which is formed on the topinsulation layer, absorbs the stresses applied to solder bumps when aCSP is mounted on a circuit board and used for an extended period, andextends the life of the solder bumps. The edge protection layer isformed on the semiconductor wafer along the scribe lines on thesemiconductor wafer, and the chip protection layer is form on the backof the semiconductor wafer. The edge protection layer and the chipprotection layer prevent external forces from damaging the CSP. Afterforming all elements of the CSP on the semiconductor wafer, thesemiconductor wafer is sawed to produce individual CSPs.

The CSP manufacturing method according to the present invention employscurrently available technology and thus, does not require development ofnew technology or equipment. Further, the wafer-level CSP manufacturingof the invention is more productive than a chip-level CSP manufacturingwhich fabricates CSPs one chip at a time after sawing a semiconductorwafer into integrated circuit chips.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 is a schematic top view of a semiconductor wafer which includessemiconductor integrated circuit chips and scribe lines formed thereon.

FIG. 2 is a cross-sectional view of a part of the semiconductor wafer inFIG. 1.

FIG. 3 shows the structure of FIG. 2 after formation of a metal layer onthe surface of the semiconductor wafer.

FIG. 4 shows the structure of FIG. 3 after formation of a patternedphotoresist layer on the metal layer.

FIG. 5 shows the structure of FIG. 4 after etching of the metal layerusing the patterned photoresist layer as a mask to produce a patternedconductor layer.

FIG. 6 shows the structure of FIG. 5 after removal of the patternedphotoresist layer.

FIG. 7 shows the structure of FIG. 6 after formation of an insulationlayer on the entire surface of the semiconductor wafer including thepatterned conductor layer.

FIG. 8 shows the structure of FIG. 7 after formation of openings so thatthe patterned conductor layer is exposed where metal bumps will beconnected to the patterned conductor layer.

FIG. 9 shows the structure of FIG. 8 after formation of a barrier layeron the entire surface of the semiconductor wafer.

FIG. 10 shows the structure of FIG. 9 after formation of anotherphotoresist layer so that the openings of insulation layer and part ofinsulation layer surrounding the openings are exposed.

FIG. 11 shows the structure of FIG. 10 after formation of intermediatebumps on the area that is not covered with the photoresist layer.

FIG. 12 shows the structure of FIG. 11 after removal of the photoresistlayer.

FIG. 13 shows the structure of FIG. 12 after removal of the barrierlayer.

FIG. 14 shows the structure of FIG. 13 after formation of a reinforcinglayer on the insulation layer and an illustrative cross-sectional viewof a CSP according to an embodiment of the invention.

FIG. 15 is a schematic bottom view of a CSP in accordance with theinvention.

FIG. 16 shows the structure after formation of a lower insulation layeron the entire surface of the semiconductor wafer except on chip pads.

FIG. 17 shows the structure of FIG. 16 after formation of an adhesionlayer on the entire surface of the semiconductor wafer.

FIG. 18 shows the structure of FIG. 17 after formation of a patternedphotoresist layer on the adhesion layer.

FIG. 19 shows the structure of FIG. 18 after formation of a patternedconductor layer on the adhesion layer where the patterned photoresistlayer is absent.

FIG. 20 show the structure of FIG. 19 after removal of the patternedphotoresist layer and the adhesion layer under the patterned photoresistlayer.

FIG. 21 shows the structure of FIG. 20 after formation of an upperinsulation layer on the entire surface of the semiconductor wafer exceptwhere solder bumps are to be formed.

FIG. 22 shows the structure of FIG. 21 after formation of a reinforcinglayer on the upper insulation layer and a illustrative cross-sectionalview of a CSP according to another embodiment of the invention.

FIG. 23 shows a part of a semiconductor wafer including an edgeprotection layer and a chip protection layer in accordance with thepresent invention.

FIG. 24 is a cross-sectional view of a CSP sawed from the semiconductorwafer in FIG. 23.

FIG. 25 is a cross-sectional view of a CSP having damage that can occurin the absence of an edge protection layer and a chip protection layer.

Use of the same reference symbols in different figures indicates similaror identical items.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides CSPs that include several features thatcan improve reliability of the packages, and a wafer-level manufacturingmethod for the CSPs.

FIGS. 2 to 14 illustrate a CSP and a method for manufacturing the CSP inaccordance with an embodiment of the present invention. Particularly,FIG. 14 shows a partial cross-sectional view of the CSP.

As shown in FIG. 1, manufacturing of the CSP in FIG. 14 begins with asemiconductor wafer 40 having a number of semiconductor integratedcircuit chips 50 and scribe lines 52 between semiconductor chips 50.FIG. 2 is a cross-sectional view of a part of semiconductor wafer 40showing a chip pad 12 and a passivation layer 14 of a semiconductor chip50. Chip pad 12 is one of many chip pads that connect to the circuitry(not shown) of semiconductor chip 50, and provides access for externalelectrical connections. Since fabrication of semiconductor wafer 40 inFIG. 1 is a well known technology, a detailed explanation of thefabrication is not made here.

With reference to FIG. 3, a metal layer 16 is formed on the entiresurface of semiconductor wafer 40 including chip pad 12 and passivationlayer 14, so that an electrical interconnection between metal layer 16and chip pad 12 is made. The thickness of metal layer 16 is greater thanthat of a metal layer (not shown) which constitutes a chip circuitpattern below passivation layer 14, and is preferably 1 to 5 μm. Metallayer 16 can be made of a various kinds of materials including, but notlimited to, copper, aluminum, nickel, copper alloys, aluminum alloys andnickel alloys.

After forming metal layer 16 on the surface of semiconductor wafer 40,patterning of metal layer 16 to form a patterned conductor layer 17follows, as illustrated in FIGS. 4 to 6. First, as shown in FIG. 4, apatterned photoresist layer 18 is formed on metal layer 16. Patternedphotoresist layer 18 covers only the area that will constitute patternedconductor layer 17. Then, etching of metal layer 16 (FIG. 5) and removalof patterned photoresist layer 18 (FIG. 6) leave patterned conductorlayer 17, which has a pattern according to a re-distribution plan ofchip pads 12.

An alternative method of forming patterned conductor layer 17 is directscreen-printing of conductor paste (not shown) on chip pad 12 andpassivation layer 14, and curing the paste to produce patternedconductor layer 17. An exemplary paste can be a mixture of metalparticles and binding resin.

FIG. 7 shows an insulation layer 24 formed on the entire surface ofsemiconductor wafer 40 after formation of patterned conductor layer 17.Insulation layer 24 becomes a part of CSP in FIG. 14, and therefore,should have desirable characteristics, for example, low moistureabsorption ratio, low dielectric constant and low thermal expansioncoefficient. Considering these properties, BCB (BenzoCycloButene) issuitable for insulation layer 24. As well as BCB, other polymers, forexample, polyimide and epoxy, and inorganic materials, for example,silicon nitride, silicon dioxide and a combination of silicon nitrideand silicon dioxide can be used for insulation layer 24. A conventionalspin-coating method can form the polymer insulation layer, and aconventional chemical vapor deposition method can form the inorganicinsulation layer. In both cases, the thickness of the insulation layeris preferably 2 to 50 μm.

Referring to FIG. 8, insulation layer 24 is partly removed to formopenings for bump pads 22, which are parts of patterned conductor layer17 exposed through the openings. Bump pads 22 can be said to bere-distributed chip pads 12, and location of bump pads 22 depends on thedesign of a board to which a CSP including bump pads 22 will besurface-mounted.

After the formation of the openings, a metallic barrier layer 26 isformed covering insulation layer 24 and bump pads 22 as shown in FIG. 9.Barrier layer 26 not only prevents the diffusion between patternedconductor layer 17 and bumps 32 in FIG. 14, but also enhances theadhesion between patterned conductor layer 17 and bump 32. Further,barrier layer 26 provides an electrical supply medium in electroplatingmetals for bumps 32 on bump pads 22. Barrier layer 26 usually includestwo or three sub-layers, and for example, includes a structure oftitanium/copper, titanium/titanium-copper/copper,chromium/chromium-copper/copper, titanium-tungsten/copper,aluminum/nickel/copper or aluminum/nickel-vanadium/copper. In formingtitanium/titanium-copper/copper or chromium/chromium-copper/copperstructure, sputtering equipment employs two targets simultaneously toform a middle titanium-copper layer or chromium-copper layer of thestructure. An adhesion layer (not shown), which has the same structureas barrier layer 26 can be formed between chip pads 12 and metal layer16 before the formation of metal layer 16 in FIG. 3. The thickness ofbarrier layer 26 and the adhesion layer is 1 μm or less, preferably0.8˜1.0 μm.

On barrier layer 26, as shown in FIG. 10, another photoresist layer 28is formed so that the openings in insulation layer 24 and areassurrounding the openings are exposed. Then, a metal for bumps 32,preferably, of a solder alloy, is plated to form intermediate bumps 30on the area that is not covered with photoresist layer 28 as FIG. 11shows. Instead of the plating method, screen-printing of solder paste,placement of pre-formed solder balls or metaljet method, which spraysliquid solder at the openings in the insulation layer, can also produceintermediate bumps 30. Before forming intermediate solder bump 30, acopper layer (not shown) can be formed several μm to tens of μm thick onbarrier layer 26 of bump pads 22 to prevent reliability problems causedby diffusion between intermediate solder bump 30 and barrier layer 26during a reflow process which melts intermediate solder bump 30 toreshape to solder bump 32.

After the formation of intermediate solder bumps 30, photoresist layer28 and barrier layer 26 are removed by etching, and only barrier metalpart 27 under intermediate solder bumps 30 remains as FIG. 12 shows.Then, a conventional reflow method reshapes intermediate solder bumps 30to solder bumps 32 as depicted in FIG. 13. In this embodiment, theheight of solder bumps 32 is between 350 μm and 500 μm.

Further, as shown in FIG. 14, a reinforcing layer 34 can be formed oninsulation layer 24 to support solder bumps 32. Reinforcing layer 34absorbs stresses applied to solder bumps 32 when CSP is mounted on acircuit board (not shown) and used for an extended period. Failurecaused by such stress is a common problem in prior CSPs For formingcover layer 34, a liquid polymer that has low viscosity can be dispensedand cured. The low viscosity of the liquid polymer allows surfacetension to draw the polymer up the side of bump 31 and creates a concavesupport of bump 32. A polymer with higher flexural strength, after beingcured, is preferable, because the higher the flexural strength is, themore stress reinforcing layer 34 can absorb from solder bumps 32.Reinforcing layer 34 should not cover the top of solder bumps 32. It ispreferable that reinforcing layer 34 meets solder bumps 32 at a pointthat is lower than the top of solder bumps 32 by ¼ of solder bumpheight.

Finally, semiconductor wafer 40 that went through the steps illustratedin FIGS. 2 to 14 is sawed along scribe lines 52 to produce individualCSPs 90 schematically shown in FIG. 15.

To provide more protection to CSPs from external shock andthermo-mechanical stresses applied to CSPs during actual use, anotherembodiment of the invention includes two insulation layers andadditional protection layers. This embodiment is described withreference to FIG. 16 to 24.

Referring to FIG. 16, a lower insulation layer 60 is formed onsemiconductor wafer 40 including chip pad 12 and passivation layer 14.After the formation of an insulation layer on the entire surface ofsemiconductor wafer 40, the insulation layer on chip pads 12 is etchedto produce openings for further interconnection. A conventional etchingmethod can remove the insulation layer on chip pads 12. Lower insulationlayer 60 becomes a part of CSP in FIG. 22, and should have desirablecharacteristics, such as low moisture absorption ratio, low dielectricconstant and low thermal expansion coefficient. Polymers such as BCB,polyimide and epoxy, and inorganic materials such as silicon nitride,silicon dioxide and a combination of silicon nitride and silicon dioxidecan be used for lower insulation layer 60. Among these, BCB is preferredfor lower insulation layer 60. The process for forming lower insulationlayer 60 is basically the same as the process for forming insulationlayer 24 as described above. The thickness of lower insulation layer 60is preferably 2 to 50 μm.

After the formation of lower insulation layer, an adhesion layer 62 isformed covering lower insulation layer 60 and chip pads 12 as shown inFIG. 17.

Adhesion layer 62 enhances the adhesion between a patterned conductorlayer 66 in FIG. 19 and chip pad 12. Adhesion layer 62 usually includestwo or three sub-layers, such as titanium/copper,titanium/titanium-copper/copper, chromium/chromium-copper/copper,titanium-tungsten/copper, or aluminum/nickel/copper. The thickness ofadhesion layer 62 is about 0.5 μm.

With reference to FIGS. 18 to 20, formation of patterned conductor layer66 is explained. First, a patterned photoresist layer 64 is formed onlower insulation layer 60 including adhesion layer 62 thereon so thatpatterned photoresist layer 64 is absent where patterned conductor layer66 will be formed. Then, a deposition method forms patterned conductorlayer 66 on adhesion layer 62 where adhesion layer 62 is exposed throughpatterned photoresist layer 64. A stripping method removes patternedphotoresist layer 64, and an etching method exposes adhesion layer 62.Patterned conductor layer 66 is made of a various kinds of materialsincluding, but not limited to, copper, aluminum, nickel, copper alloys,aluminum alloys and nickel alloys. Alternatively, forming patternedconductor layer 66 can be accomplished in a manner similar to oneexplained above with reference to FIGS. 3 to 6.

As FIG. 21 shows, after the formation of patterned conductor layer 66,an upper insulation layer 68 is formed exposing portions of patternedconductor layer 66 where bumps 74 will be formed. Subsequently, abarrier layer 72, bumps 74 and a reinforcing layer 76 are formedproducing a CSP shown in FIG. 22. The manufacturing steps from theformation of an upper insulation layer 68 to the formation ofreinforcing layer 76 are the same as the steps described with referenceto FIGS. 7 to 14. The features of upper insulation layer 68, barrierlayer 72, bumps 74 and a reinforcing layer 76 are also the same as thosedescribed above.

The embodiment can further include more protection layers: an edgeprotection layer 80 and a chip protection layer 82. FIG. 23 shows edgeprotection layer 80 formed on semiconductor wafer 40 along scribe lines52 and chip protection layer 82 formed on the back of semiconductorwafer 40. Sawing of semiconductor wafer 40 in FIG. 23 results in a CSP100 in FIG. 24. In the absence of edge protection layer 80 and chipprotection layer 82, wafer sawing and subsequent handling of CSP 100 cancreate defects in CSP 100 such as edge chipping shown in FIG. 25.

Edge protection layer 80 can be formed before the formation of bump 74by screen-printing using a mask or dotting a polymer, for example, epoxyresin, and curing the polymer. Edge protection layer 80 is preferablywider than scribe lines 52, so that part of edge protection layer 80remains on CSP 100 along the periphery as shown in FIG. 24. The heightof edge protection layer 80 is smaller than that of bump 74. It ispreferable that the height of edge protection layer 80 be smaller than{fraction (1/10)} of the height of bump 74.

Chip protection layer 82 can be formed after finishing fabrication of asemiconductor wafer by spin-coating a polymer such as polyimide andepoxy on the back of the semiconductor wafer. A preferable thickness ofchip protection layer is 2-50 μm.

CSPs made according to the present invention show many advantages overother CSPs in prior art. The advantages include enhanced solder bumpreliability, protection of CSP by an edge protection layer and a chipprotection layer, and improved manufacturability. The reinforcing layerabsorbs the stresses applied to solder bumps when the CSP is mounted ona circuit board and used for an extended period, and extends the life ofthe solder bumps and thus, the life of the CSP. The edge protectionlayer and the chip protection layer prevent the CSP from being damage byexternal force. The CSP manufacturing method according to the presentinvention employs currently available technology and thus, does notrequire development of a new technology or equipment. Further, thewafer-level CSP manufacturing of the invention is more productive than achip-level CSP manufacturing which produces a CSP after sawing asemiconductor integrated circuit chips.

Although the invention has been described with reference to particularembodiments, the description is an example of the invention'sapplication and should not be taken as a limitation. Various adaptationsand combinations of the features of the embodiments disclosed are withinthe scope of the invention as defined by the following claims.

We claim:
 1. A method for manufacturing a semiconductor package,comprising: providing a semiconductor wafer having a plurality ofsemiconductor integrated circuit chips and a plurality of scribe lines,each of the semiconductor circuit chip having a plurality of chip padsand a passivation layer thereon; forming a patterned conductor layerdirectly on the passivation layer; forming an insulation layer on thepatterned conductor layer; forming a plurality of external terminals ofthe semiconductor package; and sawing the wafer to separate thesemiconductor integrated circuit chips, wherein the patterned conductorlayer connects the chip pads to respective external terminals, and theinsulation layer includes a plurality of openings through which theexternal terminals connect to the patterned conductor layer.
 2. Themethod of claim 1, wherein forming the external terminals comprises:placing solder balls at the openings in the insulation layer so thateach solder ball sits on an associated opening; and heating the solderballs to reshape the solder balls and attach the solder balls to thepatterned conductor layer.
 3. The method of claim 1, wherein forming theexternal terminals comprises: screen-printing solder paste using a maskhaving a plurality of mask openings, each of the mask openingscorresponding to a respective one of the openings in the insulationlayer; heating the solder paste to form solder bumps attached to bumppads formed in the patterned conductor layer.
 4. The method of claim 1,wherein forming the patterned conductor layer comprises screen-printinga conductive paste and curing the paste.
 5. The method of claim 1,wherein forming the patterned conductor layer comprises plating a metallayer and etching the metal layer.
 6. The method of claim 1, wherein theinsulation layer contains a polymeric material that is selected from agroup consisting of benzocyclobutene, polyimide and epoxy resin.
 7. Themethod of claim 1, further comprising forming a chip protection layer ona back side of the semiconductor wafer.
 8. The method of claim 7,wherein the chip protection layer is formed by a spin-coating method. 9.The method of claim 1, further comprising forming a chip edge protectionlayer along scribe lines on a top surface of the semiconductor wafer.10. The method of claim 9, wherein forming the chip edge protectionlayer comprises dispensing a liquid material on the scribe lines on thewafer.
 11. A method for manufacturing a semiconductor package,comprising: providing a semiconductor wafer having a plurality ofsemiconductor integrated circuit chips and a plurality of scribe lines,each of the semiconductor circuit chip having a plurality of chip padsand a passivation layer thereon; forming a patterned conductor layerdirectly on the passivation layer; forming an insulation layer on thepatterned conductor layer; forming a plurality of external terminals ofthe semiconductor package, wherein the insulation layer includes aplurality of openings through which the external terminals connect tothe patterned conductor layer, and the patterned conductor layerconnects the chip pads to respective external terminals; forming areinforcing layer on the insulation layer, wherein the externalterminals are exposed through the reinforcing layer; and sawing thewafer to separate the semiconductor integrated circuit chips.
 12. Themethod of claim 11, wherein the reinforcing layer is formed of apolymer.
 13. The method of claim 12, wherein forming the reinforcinglayer comprises dispensing a liquid polymer for the reinforcing layerand curing the polymer.
 14. The method of claim 11, wherein thereinforcing layer is below a surface that connects the tips of theexternal terminals.
 15. The method of claim 14, wherein a perpendiculardistance from the surface to a point where the reinforcing layer meetsthe external terminals is about 100 μm.
 16. A method for manufacturing asemiconductor package, comprising: providing a semiconductor waferhaving a plurality of semiconductor integrated circuit chips and aplurality of scribe lines, each of the semiconductor integrated circuitchips having a plurality of chip pads and a passivation layer thereon;forming a lower insulation layer on the passivation layer of thesemiconductor chip, the lower insulation layer having openings over thechip pads; forming a patterned conductor layer which connects to thechip pads through the openings in the lower insulation layer; forming anupper insulation layer on the patterned conductor layer, the upperinsulation layer having openings which expose portions of the patternedconductor layer; forming a plurality of external terminals of thesemiconductor package at the openings in the upper insulation layer, theexternal terminals connecting to the patterned conductor layer, whereinthe patterned conductor layer interconnects each of the chip pads torespective external terminals; forming a reinforcing layer on the upperinsulation layer; and sawing the wafer to separate the semiconductorintegrated circuit chips.
 17. The method of claim 16, wherein the upperinsulation layer contains a polymeric material which is one selectedfrom a group consisting of benzocyclobutene, polyimide and epoxy resin.18. The method of claim 16, wherein the lower insulation layer containsa polymeric material.
 19. The method of claim 16, wherein the polymericmaterial is selected from a group consisting of benzocyclobutene,polyimide and epoxy resin.
 20. The method of claim 16, wherein the lowerinsulation layer is formed of an inorganic material.